Theorem 2.1 (Theorem 2.1 of [1]}) 

Assume that there are some non-negative constants \(\alpha _0, \alpha _1,\lambda _0, \lambda _1\)  and \(\beta _1\)  such that, for all \(v\in \mathcal {V}\)  and
\(w\in \mathcal {V}_0\) ,
\(\alpha _0\rho _A^{-1}(v,v)\le &(Rv,v)\le \alpha _1 \rho _A^{-1} (v,v), \\\lambda _0 [w,w]_{A_0}\le &[B_0A_0w, w]_{A_0}\le \lambda _1 [w,w]_{A_0},\\\Vert \Pi w\Vert _A^2\le & \beta _1 \Vert w\Vert _{A_0}^2,\) 
